Interested in Donald Trump?

"Welcome to the race Sleepy Joe. I only hope you have the intelligence, long in doubt, to wage a successful primary campaign," Trump tweeted, repeating a nickname he's tagged Biden with and questioning his intelligence and political aptitude. "But if you make it, I will see you at the Starting Gate!"

Welcome to the race Sleepy Joe. I only hope you have the intelligence, long in doubt, to wage a successful primary campaign. It will be nasty - you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate!

Former Vice President Joe Biden speaks at the International Brotherhood of Electrical Workers construction and maintenance conference in Washington, April 5, 2019.

Biden and Trump have had a tumultuous public relationship. Trump was a primary focus of Biden's announcement video, which drilled down on the president for his comments in August 2017 after white nationalists and neo-Nazis rallied in Charlottesville, Virginia.

"He said there were 'very fine people on both sides.' Very fine people on both sides?" Biden said in the video. "With those words, the President of the United States assigned a moral equivalence between those spreading hate, and those with the courage to stand against it. And in that moment, I knew the threat to this nation was unlike any I had seen in my life time."

In his tweet, Trump also tossed an insult at the rest of the 19 Democrats in the primary contest to be the party's nominee, saying Biden would be dealing with "people who truly have some very sick & demented ideas."

The president has made a habit of tweeting about his possible opponents with a false welcome to the race, including Massachusetts Sen. Elizabeth Warren, Vermont Sen. Bernie Sanders, Minnesota Sen. Amy Klobuchar and others.

It was unclear who the president was talking about or what ideas he was referring to. The Democratic primary race has covered a wide array of issues thus far, including a call from Warren for the House to initiate impeachment proceedings against the president in the aftermath of special counsel Robert Mueller's report.